1. Technical Field
This invention relates generally to piston assemblies for internal combustion engines, and more particularly to wrist pins within the assemblies.
2. Related Art
Conventional piston assemblies for use in internal combustion engines generally comprise a crown or head portion which provides a reaction surface for the combustion in a corresponding cylinder of the engine. A pair of laterally spaced pin bosses depend from the piston head and terminate in a pair of coaxial pin bores. A small end of a connecting rod is journaled about a wrist pin, and the wrist pin is journaled within the pin bores.
Typically, bushings are pressed into the pin bores and the small end of the connecting rod to provide a low friction running surface which reduces wear between the wrist pin and the journaled surfaces. However, the incorporation of bushings adds cost and complexity to the construction and manufacture of piston assemblies. As such, it has been discovered to replace the bushings in at least one of the small end of the connecting rod or the pin bores with a low-friction coating, such as disclosed in U.S. Pat. No. 7,024,981, assigned to Federal-Mogul World Wide, Inc., applicant's assignee herein. Further, it is known to incorporate hollowed wrist pins within the piston assembly to reduce weight, improve overall running performance, and extend the useful life of the assembly by reducing loads generated in use. Unfortunately, hollowed wrist pins can come with potentially adverse affects, given they are subject to increased expansion and distortion in use, due primarily to their reduced wall thickness and the affects of heat generated thereon.